Please revert the part.
buildlink3.mk should not be used if it is not required.
`required` means the package using header files or pkgconfig files from it.
buildlink add direct dependency, and adding certain ABI dependency on it too.
It seems that `zim' is pure python application, it should not be done
(or if gtk2 or depending packages's ABI is changed, zim also will be rebuilt).

Use python/distutils.mk as it should.
Use shared-mime-info/mimedb.mk as it should and remove file managed by
shared-mime-info from PLIST.

and it is nice to add graphics/hicolor-icon-theme/buildlink3.mk too.

This makes zim not abort when started.
Bump PKGREVISION.
To generate a diff of this commit:
cvs rdiff -u -r1.11 -r1.12 pkgsrc/editors/zim/Makefile
cvs rdiff -u -r1.6 -r1.7 pkgsrc/editors/zim/PLIST
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.